Since the announcement of the successful synthesis of high-aspect-ratio-few-walled boron nitride nanotubes (FW-BNNTs) in 1995, little progress had been made until very recently in the scale-up of their synthesis. In spite of the theoretical capabilities of FW-BNNTs to provide high strength-to weight, high temperature resistance, piezo actuation, and radiation shielding (via the boron content), the aerospace industry has had to rely on micron-sized graphite or boron materials for structural applications. Further, despite their very desirable properties, neither FW-BNNTs nor single wall carbon nanotubes are used widely in aerospace manufacturing and similar industries, as industries are generally unwilling to pay the premium price for these high performance materials.
Prior to recent inventions of the present inventors, high-aspect ratio FW-BNNTs had only been produced in small amounts (from individual tubes to milligrams) by arc-discharge or laser heating methods. Further, these small amounts of FW-BNNTs were in the form of films not strands or fibers several centimeters in length. A separate class of boron nitride nanotubes know in the prior has been produced by chemical vapor deposition of nitrogen compounds (e.g. ammonia) over ball-milled precursors, but these tubes are of large diameter, and do not exhibit the continuous crystalline sp2-type bonding structure which has drawn most theoretical interest.
The Inventors' recent work in the field of boron nitride nanotubes is described in three US. Patent Applications including U.S. patent application Ser. No. 12/152,414 filed May 14, 2008, U.S. patent application Ser. No. 12/322,591 filed Feb. 4, 2009, and U.S. patent application Ser. No. 12/387,703 filed May 6, 2009, all of which are incorporated herein by reference in their entireties, and Inventor's article “Very Long Single- and Few-walled Boron Nitride Nanotubes Via the Pressurized Vapor/condenser Method” by Smith, Jordan, Park, Kim Lillehei, Crooks and Harrison; Nanotechnology 20 (2009) 505604. Inventors' U.S. patent application Ser. No. 12/152,414, describes the generation of very long single- and few-walled boron nitride nanotubes (BNNT) via a pressurized vapor/condenser method. In the pressurized vapor/condenser method few walled boron nitride nanotubes fibers grow continuously by surface nucleation from seemingly arbitrary asperities at a high linear rate (many cm per sec) in the line of flow of vaporized boron produced from a solid boron containing target mixed with nitrogen under elevated pressures.
Boron nitride nanotubes have electrical insulating properties in contrast to carbon nanotubes which are electrical conductors. This means that boron nanotubes with insulating properties have very different potential applications than carbon nanotubes which conduct. Accordingly, nanotubes, which combine boron nitride with carbon, are of considerable interest because of their potential as semiconductors.
While the pressurized vapor/condenser method has significant advantages over the prior art the energy efficiency of the pressurized vapor/condenser method is relatively low due to a large loss of heat to the solid boron support that is used both to supply and support the boron target being vaporized by the heat source (laser) driving the process.
Hence a method for producing boron nitride nanomaterials in a more energy efficient manner is highly desirable.